Well, you have to weigh the incredible ease of just bolting the SU's on to the not trivial task of installing all the D-Jet electricals and extra plumbing.

All in all I'd have to say that D-Jet (in my experience) is a cleaner running, less tweaking and slightly more powerful setup. My thought is that D-Jet vs. SU's on an identical engine (well, stock at least) will make slightly more power due to the tuned plenum and 4 long straight wide open intake runners. I think that manifold adds a little more low-to-mid range torque.

However, SU's can be tweaked to keep up with a modified engine somewhat more easily, at least using the skill sets most of us shade tree mechanics have. The advantage D-Jet would have is that with all the 'infrastructure' already on the car you are that much closer to putting a modern programmable FI system like Megasquirt on.